This disclosure relates to vehicle control for an autonomous or semi-autonomous vehicle or a vehicle with high degree of driving automation. Some vehicles are configured to operate autonomously, with no input required by the driver. Instead, the vehicle systems are controlled by a computing device associated with the vehicle, using information about the vehicle's movement and the surrounding driving environment provided by various sensors disposed on or otherwise affixed to various points on the vehicle. In related technology, some vehicles are configured to operate semi-autonomously, in which the driver controls only certain aspects of the vehicle operation, such as steering, while the computing device controls other aspects of the vehicle operation, such as braking and acceleration, also using information about the vehicle's movement and the surrounding driving environment received from the sensors.
It has been recognized that some driving environments that the vehicle encounters are too complex or hazardous to rely exclusively on the autonomous systems. In such a case, the vehicle may be able to determine that an unexpected driving environment has been encountered, for which the vehicle is ill equipped to handle, based on the data captured by the vehicle sensors. Various methods have been suggested as to what criteria should be used in making such a determination, for example, U.S. Pat. No. 8,718,861 to Montermerlo et al. Some have suggested that in such a case, the computing device should stop operating the vehicle autonomously and alert the driver that the driver must manually operate the vehicle. However, this could disturb the driver, who would rather not have to control the vehicle.